edison



(No Model.)

T. A. EDISON. PROCESS OF COATING OONDUOTORS FOR INGANDESGENT LAMPS.

No. 492,150. Patented Feb. 21, 1893.

T T: I V INVENTOR:.

ATENT OFFICE.

THOMAS A. EDISON, OF MENLO PARK, NEW JERSEY, ASSIGNOR TO THE EDISONELECTRIC LIGHT COMPANY, OF NEW YORK, N. Y.

PROCESS OF COATlNG CONDUCTORS FOR INCANDESCENI LAMPS.

SPECIFICATION formingpart of Letters Patent No. 492,150, dated February21, 1893.

Application filed October 26, 1882. Serial No. 75,204. (No specimens.)

To all whom it may concern:

Be it known that I, THOMAS A. EDISON, of Menlo Park, in the county ofMiddlesex and State of New Jersey, have invented a new and usefulImprovementin Processes of Coating Conductors for Incandescent Lamps,(Case No. 503,) of which the following is a specification.

The object of my invention is to prevent the electrical carrying whichoccurs in incandescing electric lamps; that is, the transferring bystatic attraction, of highly electrified particles of carbon from theincandescing filament to the oppositely-charged glass of the inclosingglobe.

To this end my invention consists in the process of covering theflexible carbon filament of an incandescing electric lamp with a coatingof insulating material not decomposable by carbon, and fusible at thehighest temperatures only. For this purpose I prefer to use one of theearthy oxides, such as lime, magnesia, or zirconia, I having discoveredthat such oxides cannot be decomposed by carbon except in the presenceof watery vapor which of course does not occur in 'the vacuum chambersof incandescing electric lamps; but boron, silicon or like elements maybe used, these being sufficiently good insulators or bad conductors forthe purpose, or any element or compound which possesses the propertiesmentioned. The effect of this coating of the filament is that the staticattraction will draw over particles of the oxide or other materialinstead of particles of carbon. The insulation will become incandescentfrom its contact with the heated filament, and the light will thereforenot be lessened.

I have devised several different processes which may be advantageouslyemployed for covering the filament with a durable and continuous coatingof insulation. By one method, the filament which in this case ispreferably straight, is placed in a glass tube with platinum wiresconnected to its ends,

such wires being sealed in the glass of the tube. The tube is thenfilled with an oxide such as those named above, in a finely dividedcondition, and packed closely around the filament. Means are providedfol-producing a vacuum in the tube, and during the ex- The filament socoated, is placed in the lamp globe and the latter is exhausted andsealed off in the usual manner.

Instead of exhausting the tube WhlGhOOlltains the oxide it may be filledwith nitrogen or other nearly inert gas the same eifect being produced.

In the case where the tube is exhausted,

said tube may be heated in a flame so that the glass is softened and thetube will c011- tract under the pressure of the atmosphere upon theoxide, pressing it closely against the filament. The whole may then beplaced in the inclosing lamp-globe.

The process described is illustrated in the drawing, wherein a is theflexible carbon filament having wires b I) attached to its ends andsealed in the glass of the tube A. Within the tube A is packed thefinely divided oxide 0. A tube at is used to connect the tube A with anexhausting apparatus.

What I claim is 1. The process-of coating a flexible carbon filamentdesigned for the incandescing conductor of an electric lamp, withinsulating material, consisting in heating said filament while in a massof such material, thereby fusing a layer of such material to saidfilament, substantially as set forth.

2. The process of coating a flexible carbon filament, designed for theineandescing conductor of an electric lamp, with insulating materialconsisting in embedding such conductor in an insulating oxide 01'compound in a suitable receptacle, exhausting air therefrom, and finallypassing a current through said filament sufficient to fuse a coating ofsuch oxide onto the filament, substantially as set forth.

This specification signed and witnessed this 19th day of October, 1889.

TI'IOS. A. EDISON.

itnesses:

II. W. SEELY, EDWARD 1T. PYATT.

